The invention relates to a device for assisting the cardiac function, and particularly to a device that assists the heart to pump blood when the heart is in a weakened state.
When a patient is suffering from a cardiac dysfunction, for example a disease such as dilatory cardiomyopathy, or an infection causing myocarditis, or is recovering from cardiac surgery, it is common practice to connect the patient to an external system that assists the ventricular function. Typically, these systems remove blood from the patient's pulmonary vein or left atrium through a tube, direct the blood to an external pump, and then return the blood, now at a higher pressure, to the patient's aorta. The heart assist system therefore reduces the amount of blood that the left ventricle is required to pump through the patient's body, thus reducing the load on the left heart to permit the heart's recovery.
Since such heart assist systems are external to the patient, there are several problems and disadvantages. The heart assist system is generally bulky, and has to be transported along with the patient whenever the patient is moved. Therefore, the patient is usually immobile when attached to the heart assist system. The heart assist system uses an external pump with flexible tubes inserted through the skin and into the heart and the aorta: the points at which these tubes enter the patient's body are possible centers of infection. There may also be problems of bleeding where conventional tubes are connected with the left heart and aorta due to relative motion between the anastomosis and point of entry on the patient's skin.
If the patient is attached to an external heart assist system for a long time, there is a risk of myocardial atrophy. Moreover, when it is time to remove the patient from the heart assist system, a second surgical procedure is necessary to remove the tubes inserted into the heart.
A recently developed heart assist device includes a pump that is placed within the patient's left ventricle using a catheter passing through the femoral artery. The pump is rotated by a wire passing within the catheter which is attached to a an external motor. However, since the catheter passes through the aortic valve, the valve is unable to close completely while the pump is in place. Additionally, the patient has to remain stationary while the pump is in position because of the rigid wire passing through the catheter. This requires the patient to be heavily sedated throughout the time the pump is in place. Typically such a pump remains within the patient for 2-7 hours, but may be used for up to 48 hours before the pump's efficacy is reduced due to use.
Thus, the choices faced by doctors and patients currently require that the patient either be heavily sedated during the period of use of the heart assist system, or that the patient undergo two surgical procedures, a first to implant the system and a second to extract the system after use so that the patient may regain mobility. Further, since the patient's mobility is impaired by all conventional heart assist devices, the doctor may be faced with the dilemma of taking a patient off the heart assist device before recovering full cardiac function in order to allow the patient to be mobile. This may be a particular problem when the patient's cardiac function takes several days or more to recover.
Therefore, there is a need to develop a heart assist device that avoids such a dilemma, and permits the patient to be mobile even when the device is in use. Also, there is a need to develop a heart assist device that reduces the chance of infection and which requires neither that the patient be heavily sedated during use, nor that the external device be removed after use by a surgical procedure.